Annular combustion chamber for a turbine engine including improved dilution openings

TECHNICAL FIELD

0001This invention relates to the field of annular combustion chambers for turbine engines like those used on aircraft.

0002It more particularly concerns dilution air inlet orifices formed in the coaxial walls of these combustion chambers.

STATE OF PRIOR ART

0003Turbine engines comprise at least one turbine arranged downstream from a combustion chamber to extract energy from a primary flow of gases ejected from this combustion chamber and drive a compressor arranged upstream from the combustion chamber and supplying this chamber with high pressure air.

0004The appended <figref idref="DRAWINGS">FIG. 1</figref> shows a typical example of a turbine engine combustion chamber <b>10</b> comprising two coaxial annular walls, one radially inner wall <b>12</b> and one radially outer wall <b>14</b>, that extend from the upstream side towards the downstream side along the flow direction <b>16</b> of the primary gas flow in the turbine engine, about axis <b>18</b> of the combustion chamber, and that are connected to each other at their upstream end by an annular chamber bottom wall <b>20</b> that extends approximately radially around the above-mentioned axis <b>18</b>. This annular chamber bottom wall <b>20</b> is fitted with injection systems <b>22</b> distributed around this axis to bring air and fuel into the combustion chamber.

0005In general, combustion chambers are composed of an upstream internal region <b>24</b> usually called the primary zone, and a downstream internal region <b>26</b> usually called the dilution zone.

0006The primary zone <b>24</b> of a combustion chamber is designed for combustion of the air and fuel mix and is supplied with air not only through the injection systems <b>22</b> but also through air inlet orifices <b>28</b>, currently called primary orifices, formed in the coaxial walls <b>12</b> and <b>14</b> of the chamber around the primary zone <b>24</b> of this chamber, in one or several annular rows.

0007The dilution zone <b>26</b> is designed to dilute and to cool gases derived from combustion in the primary zone, and to confer an optimum temperature profile onto the flow of these gasses as they pass through the turbine mounted downstream from the combustion chamber. To achieve this, the coaxial walls <b>12</b> and <b>14</b> of the combustion chamber comprise at least one row of air inlet orifices <b>30</b> on the downstream side of the above mentioned primary orifices <b>28</b>, usually called dilution orifices.

0008During operation, a part <b>32</b> of an airflow <b>34</b> originating from a compressor outlet <b>36</b> supplies the injection systems <b>22</b> while another part <b>38</b> of this airflow bypasses the combustion chamber and flows in the downstream direction along the coaxial walls <b>12</b> and <b>14</b> of this chamber and in particular supplies the primary orifices <b>28</b> and the dilution orifices <b>30</b>.

0009As shown in the appended <figref idref="DRAWINGS">FIG. 2</figref> that shows a developed plan view of a part <b>31</b> of the annular wall of the combustion chamber including an annular row of dilution orifices <b>30</b> with a circular section, these orifices conventionally include orifices <b>40</b> with a larger cross-sectional area and orifices <b>42</b> with a smaller cross-sectional area.

0010Each of the dilution orifices <b>40</b> with the larger area may for example be centred relative to the axis <b>44</b> (<figref idref="DRAWINGS">FIG. 1</figref>) of a corresponding injection system <b>22</b>, while the dilution orifices <b>42</b> with the smaller area are inserted between the orifices <b>40</b> with the larger area and for example there may be three times as many of them as the larger orifices (<figref idref="DRAWINGS">FIG. 2</figref>).

0011It is usually necessary to cool the coaxial annular walls <b>12</b>, <b>14</b> of the combustion chambers, taking account of the high temperatures reached by gases during combustion.

0012Multi-perforation is a known technique for achieving this, and consists of the formation of a plurality of micro-perforations <b>46</b> (<figref idref="DRAWINGS">FIG. 2</figref>), in other words small orifices with a diameter of about 0.6 mm, normally with an inclined axis, in some regions of the coaxial walls <b>12</b>, <b>14</b> of the combustion chambers. Part of the relatively cool airflow <b>38</b> bypassing these combustion chambers can penetrate into them through these micro-perforations and form a cooling air film along the internal faces of the coaxial walls <b>12</b> and <b>14</b> of these combustion chambers.

0013However during operation, the coaxial walls <b>12</b>, <b>14</b> of the combustion chambers expand as their temperature increases and high vibrations are applied to them, that can create high stresses that can cause the appearance of cracks or fissures, particularly at the edges of the dilution orifices <b>30</b>.

0014A minimum separation between the dilution orifices <b>30</b> and a perimeter without any micro-perforations around each of these orifices are usually provided to limit the risks of development and extension of such cracks.

0015Furthermore, since the micro-perforations <b>46</b> are usually arranged in homogeneous rows with uniformly spacing along the axial direction, a minimum axial spacing is also provided between these rows of micro-perforations <b>46</b>.

0016However, respecting said perimeter without any micro-perforations around the dilution orifices <b>30</b> means that some peripheral zones around these orifices are not optimally cooled, particularly concerning the smallest area orifices <b>42</b>, and particularly when the micro-perforations <b>46</b> are arranged in uniformly spaced rows along the axial direction.

0017This problem is shown in <figref idref="DRAWINGS">FIG. 2</figref> that shows two annular rows of micro-perforations <b>46</b>, the upstream row <b>48</b> and the downstream row <b>50</b> formed on the upstream and downstream sides respectively of the annular row of dilution orifices <b>30</b>, and three intermediate rows <b>52</b> of micro-perforations <b>46</b> that are arranged between the upstream row <b>48</b> and the downstream row <b>50</b> mentioned above and that are interrupted by dilution orifices <b>30</b>, the constant axial spacing between two consecutive rows of micro-perforations <b>46</b> being marked d in this figure.

0018Respecting said perimeter without any micro-perforations induces the existence of relatively large and extended zones without micro-perforations, at the upstream part <b>54</b> and the downstream part <b>56</b> of the periphery of each of the dilution orifices <b>42</b> with the smaller area, which can result in insufficient cooling of the upstream part <b>54</b> and the downstream part <b>56</b>.

PRESENTATION OF THE INVENTION

0019In particular, the purpose of the invention is to simply, economically and efficiently improve cooling of the periphery around dilution orifices of a combustion chamber, to at least partially avoid the above mentioned disadvantages.

0020To achieve this, the invention discloses an annular wall for an annular turbine engine combustion chamber comprising at least one annular row of dilution air inlet orifices comprising two types of orifices differentiated by their cross-sectional area, namely orifices with a larger area and orifices with a smaller area, as well as a multi-perforation for cooling said wall, said multi-perforation being formed from micro-perforations that have a cross-sectional area less than the area of each of said dilution air inlet orifices and that are distributed as an upstream annular row and a downstream annular row formed on the upstream side and downstream side respectively of said row of dilution air inlet orifices, and as at least one intermediate annular row interrupted by these dilution air inlet orifices, a geometric ratio being defined for each of the dilution air inlet orifices as the quotient obtained by dividing the maximum spacing between any two points on the edge of this orifice measured along a direction parallel to an axis of revolution of the wall, by the maximum spacing between any two points on the edge of this orifice measured along a direction perpendicular to this axis.

0021According to the invention: <ul id="ul0001" list-style="none"><li id="ul0001-0001" num="0000"><ul id="ul0002" list-style="none"><li id="ul0002-0001" num="0022">the above mentioned geometric ratio is greater than or equal to 1, for said dilution air inlet orifices with the larger area, and</li><li id="ul0002-0002" num="0023">this geometric ratio of said dilution air inlet orifices with the smaller area is greater than the geometric ratio of said dilution air inlet orifices with the larger area.</li></ul></li></ul>

0024The conformation of the dilution air inlet orifices with the smaller area is such that the upstream and downstream rows of micro-perforations in the upstream and downstream parts can be brought closer to the edges of these orifices and therefore zones without any micro-perforations that occur in known types of walls as explained above, can be reduced or even eliminated. The result is more uniform cooling around the periphery of these orifices.

0025Furthermore, conformation of the dilution air inlet orifices with the smaller cross-sectional area is such that a sufficient circumferential separation can be maintained between all the dilution orifices, and this spacing can even be increased in some cases, for example between two adjacent orifices with the smaller area or between an orifice with the larger area and an orifice with the smaller area adjacent to each other.

0026Maintaining the circumferential spacing between adjacent dilution orifices can limit the risks of cracks or fissures appearing at the edge of these orifices.

0027The increase in the circumferential spacing between adjacent dilution orifices also makes it possible to increase the circumferential range of the angular sectors of intermediate rows of micro-perforations formed between these orifices, and therefore to further improve cooling provided by the multi-perforation.

0028In one preferred embodiment of the invention, the dilution air inlet orifices with the larger area are circular in shape and the dilution air inlet orifices with the smaller area are oval in shape.

0029In this case, the geometric ratio mentioned above is equal to 1 for the dilution air inlet orifices with the larger cross sectional area.

0030The edges of the dilution air inlet orifices of both types advantageously have upstream and/or downstream ends that are circumferentially in line with each other.

0031Such configuration can minimise differences in cooling between the two types of dilution air inlet orifices.

0032In the preferred embodiment of the invention, each intermediate annular row of said multi-perforation is interrupted by both types of dilution air inlet orifices.

0033Multi-perforation thus enables optimum cooling of all of these dilution air inlet orifices.

0034As a variant, some intermediate rows may be interrupted only by the larger area dilution orifices when this is useful.

0035Furthermore, the axial spacing between each pair of consecutive rows among said upstream, downstream and intermediate annular rows of said multi-perforation is preferably equal to a constant predetermined value.

0036Such uniformity in the arrangement of the micro-perforations, which is known in itself, particularly facilitates formation of these micro-perforations.

0037The invention also relates to an annular combustion chamber for a turbine engine comprising two coaxial annular walls, namely an inner wall and an outer wall, connected to each other by an annular chamber bottom wall, at least one of which is of the type described above.

0038The invention also relates to a turbine engine comprising an annular combustion chamber of the type mentioned above.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and other details, advantages and characteristics of it will become clear after reading the following description given as a non-limitative example with reference to the appended drawings in which:

<figref idref="DRAWINGS">FIG. 1</figref>, already described, is a partial diagrammatic view of an axial section of a turbine engine combustion chamber of a known type;

<figref idref="DRAWINGS">FIG. 2</figref>, already described, is a partial developed diagrammatic plan view of an annular wall of the combustion chamber in <figref idref="DRAWINGS">FIG. 1</figref>;

<figref idref="DRAWINGS">FIG. 3</figref> is a view similar to <figref idref="DRAWINGS">FIG. 2</figref>, of an annular combustion chamber wall according to the invention.

0043Identical references are used to denote identical or similar elements in all of these figures.

DETAILED PRESENTATION OF A PREFERRED EMBODIMENT

0044<figref idref="DRAWINGS">FIG. 3</figref> shows part of an annular wall <b>60</b> that will form the inner wall or the outer wall of a turbine engine combustion chamber similar to the combustion chamber in <figref idref="DRAWINGS">FIG. 1</figref> described above.

0045This annular wall <b>60</b> is different from the known type of wall shown in <figref idref="DRAWINGS">FIG. 2</figref> due to the conformation of its dilution air inlet orifices with the smaller cross-sectional area <b>62</b> and by the configuration of micro-perforations <b>46</b> of this wall.

0046The dilution air inlet orifices with the smaller cross-sectional area <b>62</b> are oval in shape, and have a large axis approximately parallel to the axis of revolution of the combustion chamber.

0047On the other hand, since the dilution air inlet orifices with the larger cross-sectional area <b>40</b> are similar to those of the wall in <figref idref="DRAWINGS">FIG. 2</figref>, the dilution air inlet orifices with the smaller area <b>62</b> have an area approximately identical to the area of the dilution air inlet orifices with the smaller area <b>42</b> in <figref idref="DRAWINGS">FIG. 2</figref>.

0048The oval shape of the orifices <b>62</b> can increase the circumferential range of each angular sector <b>64</b> of the intermediate rows <b>52</b> of micro-perforations <b>46</b>, particularly for angular sectors located between two adjacent orifices with the smaller area <b>62</b>.

0049This oval shape can also increase the global density of micro-perforations <b>46</b> around the periphery of each dilution orifice with the smaller cross-sectional area <b>62</b>, and in particular can avoid the existence of zones without any micro-perforations around this perimeter, such as the zones <b>54</b> and <b>56</b> in <figref idref="DRAWINGS">FIG. 2</figref>.

0050The oval shape of the orifices <b>62</b> is only one example conformation of orifices among many possibilities in which the quotient obtained by dividing the maximum spacing L between any two points on the edge of each orifice measured along a direction parallel to the axis of revolution <b>18</b> (<figref idref="DRAWINGS">FIG. 1</figref>) of the wall by the maximum spacing I between any two points on the edge of this orifice measured along a direction perpendicular to this axis <b>18</b> is greater than or equal to 1, as regards the orifices <b>40</b> with the larger area, and is greater than the quotient for said orifices <b>40</b> with the larger cross-sectional area, as regards orifices <b>62</b> with the smaller cross-sectional area.

0051In the example shown in <figref idref="DRAWINGS">FIG. 3</figref>, the upstream ends <b>66</b> and downstream ends <b>68</b> of the dilution orifices <b>40</b> and <b>62</b> of the two types are in line circumferentially, for optimum cooling uniformity.